Aircraft are constantly operating in close proximity of other aircraft and, on the ground, also in close proximity of other vehicles and obstacles. Separation from such hazards, therefore, is of prime importance in assuring the safe continuation of a flight. In flights operating under Visual Flying Rules (VFR), the responsibility of separation lies with the pilot. Separation is normally ensured through good situational awareness of traffic in the vicinity of the ownship. This is traditionally achieved by keeping a good look-out and through radio communication, which allows the crew to build a mental picture of the traffic movements in the vicinity. Under Instrument Flying Rules (IFR), separation is the responsibility of air traffic control (ATC), where the air traffic control officer (ATCO) directs traffic in such a way to ensure safe separation between all entities.
In controlled airfields, the ATCO is responsible for the control of traffic in and around the airfield and it is the ATCO who provides clearances for aircraft to enter a runway, take-off or land. It is therefore the ATCO who ensures that any movements are well clear of the particular aircraft in take-off or landing. In essence, the ATCO reserves the runway (or a portion of it) for the exclusive use of this aircraft and procedures are rigorously followed to ensure safe separation from other aircraft. Nevertheless, it is good airmanship for pilots to independently ensure that they are cleared to enter a runway, land on it or take-off, that the approaches of a runway are indeed clear before entering it and, before taking off or landing, that the runway itself is clear. Such actions are, of course, more effective in situations of good visibility and in reduced visibility and bad weather, pilots and ATCOs are more careful to ensure that separation is indeed maintained. In fact, reduced visibility operations are subject to more stringent separation rules, where separation between aircraft is intentionally increased and certain manoeuvres are not allowed.
Therefore, whereas the procedure dictates that the ATCO is responsible for traffic separation, the pilot also plays an active role in ensuring that the required separation is indeed preserved. The pilot also plays a critical role in restoring this separation when it is lost and this role is essential for the mitigation of the risk of collision.
Positional and traffic situational awareness are fundamental in maintaining safe separation between aircraft and this is generally achieved through good communication on voice radio, which allows the relevant parties to build a mental picture of all movements in the vicinity.
However, notwithstanding rigorous procedure, training and good practice, the current procedural method of maintaining separation is prone to failure. This repeatedly results in aircraft (and vehicles) coming in conflict with one another on the runway. Indeed, in the US alone, during the period 2003 to 2006, 1306 runway incursions have been reported [FAA Runway Safety Report, September 2007, Federal Aviation Administration]. The FAA then defined runway incursion as any occurrence in the airport runway environment involving an aircraft, vehicle, person or object on the ground that creates a collision hazard or results in a loss of required separation with an aircraft taking off, intending to take off, landing or intending to land. In October 2007, the FAA adopted the ICAO definition, which defines a runway incursion as any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle, or person on the protected area of a surface designated for the landing and take-off of an aircraft.
Current procedure, therefore, can be considered unsatisfactory and needs to be complemented by a means that monitors traffic in the vicinity and warns the pilot accordingly. In a way, a sort of ‘electronic-supervisor’ is required in order to complement the pilot (or ATCO) and to provide appropriate advice when he or she fails to see or detect the conflict.